Back to topic: Your teacher is ignorant. Now, how do you point that out and prove it.

I'd go to the school library, find a decent and accurate account of any of those battles, particularly Agincourt. Copy the relevant pages, highlight "longbows" and other relevant words, and leave them anonymously upon her desk.

Unfortunately, this is not an aberration. I have one daughter here in Fayetteville and another living with her mom in a town more than 200 miles away. Both have had history teachers who are late-career coaches waiting for retirement. One daughther's ancient and medieval history class consisted of hearing old war stories from Vietnam for the first 9 weeks. The other just talked about how much he hated then-president Bill Clinton. In my own schooling, I corrected the teacher in front of the whole class when she got the starting YEAR of the Second World War wrong.